This invention relates to an improvement in apparatus for continuous metal casting, or the so-called "dip forming process" of metal casting. The apparatus includes a crucible or refractory container for molten metal which is provided with an entry port or orifice for the introduction and passage of a core member into the crucible or container and through the molten metal contained therein. A bushing member of refractory metal is inserted in the entry port or orifice or provide a relatively wear resistant seal about the moving core member.
The dip forming process of continuously casting by means of passing a core member upwardly through a crucible of molten metal, and apparatus therefor, is the subject of many prior U.S. patents, including:
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The disclosures of these U.S. patents are incorporated herein by reference.
The dip forming process of continuously casting as heretofore practiced and provided for by prior art apparatus, incurred a serious defect in the form of the introduction of contaminating bodies of foreign metal or material into the cast product. The most common source of such bodies of foreign metal or material within the cast product, referred to in this art as "inclusions", appears to be the bushing member in the entry port in the crucible bottom which is utilized as a close fitting seal about the core member as it moves therethrough into the molten contents of the crucible. It appears that particles separate from the bushing member, which is typically composed of a hard refractory material such as sintered molybdenum, and penetrate the core member moving therethrough. These embedded foreign particles or bodies in the core member are then carried through the casting operation wherein they may become completely enveloped within the cast product.
The presence of particles of any foreign metal or other material from the bushing member, or whatever the source, in cast metal products comprises a substantial detriment in subsequent metal working operations such drawing, rolling, forging, extruding, and the like, and in the products derived therefrom. Moveover, the dip forming process of continuously casting is primarily utilized in commercial manufacturing operations for the production of copper rod for use in drawing electrical conducting wires. The existence of any foreign particles, and especially of a very hard material such as molybdenum, in copper rods presents an especially serious impediment in the drawing of wire inasmuch as their presence causes frequent breakages in the extending strands, thereby disrupting the production system, or resulting in weakened and inferior wire products. Also, the passage of relatively hard particles such as molybdenum entrained in copper through drawing dies or reducing rolls, and other metal working apparatus, is detrimental to such equipment.